1. Field of the Invention
The present invention relates to an image processing apparatus and method and, more particularly, to an image processing apparatus and method for processing an image sent from an external apparatus such as a host computer or the like, and an image read from an original.
2. Description of the Related Art
An image forming system which is constructed by a controller for receiving image data from a host computer and sending the received image data to an image forming apparatus, and an image forming apparatus for forming an image on the basis of the image data sent from the controller is known. For example, an image forming system as combination of a CLC500 (tradename) color copying machine as an image forming apparatus and various controllers is commercially available. This color copying machine is a laser beam type color electrophotographic printer which frame-sequentially forms images in correspondence with a plurality of output color components C (Cyan), M (Magenta), Y (Yellow), and K (Black), and realizes halftone expression by controlling laser beam emission by a signal pulse-width-modulated in accordance with an image signal.
In such image forming apparatus, a technique for stabilizing the quality of an output image via density correction and gradation correction by forming a predetermined pattern on an image carrier or recording medium, and reading the density of the formed predetermined pattern is known.
However, the aforementioned technique suffers the following problems.
An image output by reading an original image by the color copying machine alone as the image forming apparatus (to be referred to as a “copy image” hereinafter), and an image output based on image data sent from the controller (to be referred to as a “print image” hereinafter) are not yet sufficiently standardized in terms of their density and gradation reproducibility.
A calibration system which adjusts the density and gradation reproducibility of a print image using an expensive densitometer is known. However, calibration that uses a reader/scanner of the color copying machine is not performed.
Furthermore, calibration that takes a color sample used as a standard into consideration is made, but no image adjustment corresponding to the color sample is made.
On the other hand, variations of the image density and gradation reproducibility include a short-term variation resulting from a variation of the apparatus environments, a long-term variation resulting from aging of a photosensitive body and toner, and the like. In order to standardize the density and gradation reproducibility of a copy image and print image, such variations must be corrected together.